Method and device for loading a fibrous stock suspension

ABSTRACT

The present invention relates to a method and a device for loading a fibrous stock suspension including a plurality of cellulose fibers with calcium carbonate. The method includes adding calcium hydroxide in liquid or dry form and/or calcium oxide into the fibrous stock suspension, adding carbon dioxide into the fibrous stock suspension, and precipitating calcium carbonate from calcium hydroxide through carbon dioxide in a pressurized vessel.

BACKGROUND OF THE INVENTION

This is a continuation of PCT application No. PCT/EP2005/008851, entitled “METHOD AND DEVICE FOR CHARGING A FIBRE MATERIAL SUSPENSION”, filed Aug. 16, 2005.

1. Field of the Invention

The invention relates to a method for loading of a fibrous stock suspension with calcium carbonate.

2. Description of the Related Art

Several methods for loading chemical pulp fibers with calcium carbonate are already known. A method is described in U.S. Pat. No. 6,413,365 B1 where the fibrous material is transported via a supply line together with calcium oxide and/or calcium hydroxide which are contained in said suspension. From there, the fibrous stock suspension is transported into a rotating distribution device. A reaction gas is fed in a ring shaped pattern into the fibrous stock suspension; this causes formation of calcium carbonate crystals in the fibrous suspension. The calcium carbonate crystals are distributed in the fibrous stock suspension through the rotating distributor device. This process is known as Fiber Loading Process.

A method for loading a fibrous stock suspension is known from DE 101 07 448 A1 wherein the fibrous stock suspension is fed into a crystallizer and is treated in said crystallizer by shear forces in order to break down larger fiber agglomerates into smaller ones, or even into individual fibers, and wherein the crystallizer is utilized at the same time as reactor for the chemical precipitation reaction.

What is needed in the art is to further simplify a method for loading of a fibrous stock suspension with calcium carbonate.

SUMMARY OF THE INVENTION

The present invention provides a method including the following process steps: adding of calcium hydroxide in liquid or dry form, or of calcium oxide into the fibrous stock suspension; adding of carbon dioxide into the fibrous stock suspension; and precipitation of calcium carbonate from the calcium hydroxide through the carbon dioxide in a pressurized pressure vessel.

The current invention describes a method for the production of fiber loaded precipitated calcium carbonate (FLPCC), wherein the fiber raw material that is to be loaded may include recycling paper, DIP (deinked paper), secondary fibers, bleached or unbleached pulp, mechanical pulp, bleached or unbleached sulfate pulp, broke, linen, cotton, and/or hemp fibers (predominantly cigarette paper) and/or any paper raw material which can be utilized on a paper machine.

With the method according to the current invention the currently used filler material is replaced, supplemented or activated by the filler material which is produced by the fiber loading process technology. Activation means that the already existing filler particles are superimposed by the fiber loading process or serve as a crystallization nucleus, thereby providing improved optical characteristics.

The method is also especially suitable if paper which is printed with flexo-ink (water based printing ink)—especially news print—is used for the production of the fiber raw material. The print particles including flexo-ink cannot be removed through a floatation process, or can be removed only with great difficulty. With the current invention it is now possible to integrate fillers and foreign substances such as printing ink, contaminants, stickies, etc., which are inherently present in DIP papers into the fiber loading-crystallization process wherein the already present filler particles are being superimposed by the fiber loading process, or serve as crystallization nucleus.

The method is independent of whether or not the fiber raw material contains a filler that was produced by a precipitation process in a batch reactor or by a refining process, or whether talcum, titanium dioxide (TiO₂), silicon, etc., are used. The refining process is also referred to as GCC-process (GCC=ground calcium carbonate).

When a fibrous stock suspension is processed with the fiber loading technology, a completely new product for application in paper production will result, with new and improved characteristics compared to a product according to the current state of the art. The fiber loading technology permits precipitation of a filler—especially calcium carbonate—that is uniformly distributed and adhered to, in and between the fibers directly in the stock preparation of a paper mill.

The range of application of the filler produced with the fiber loading combination process technology extends to applications within the paper production of all paper grades, including cigarette papers, filter papers, kraft sack paper grades and cardboard and packaging papers including those with which recycling paper types and DIP papers are used. Packaging papers of this type can have a filler content of between 1 and 60% and/or can possess a white liner having a filler content of between 1 and 60%. The loaded and manufactured paper grades can be produced on a paper machine from a recycling paper, deinked paper (DIP), secondary fibers, bleached or unbleached pulp, mechanical pulp, bleached or unbleached sulfate pulp, broke, linen, cotton, hemp fibers (predominantly for cigarette paper), and/or any paper raw material, irrespective of whether or not the end product contains a filler.

Fibrous stock produced according to the fiber loading combination process technology generally possesses a superior dewatering characteristic compared to a fibrous stock produced according to another method; the dewatering capacity is between 5 to 100 ml CSF or 0.2 to 15° SR, depending upon the required freeness. The stock or pulp produced according to the fiber loading process further possesses a lower water retention value of 2 to 25% depending upon the raw material used in the production process. This permits a more effective production of various paper grades, for example FL (FL=fiber loaded) copy and printing paper of all types, FL coating paper of all types, FL news print of all types and FL cigarette paper of all types, FL B&P paper of all types, FL kraft sack paper of all types and FL filter paper, since the water in the stock suspension can be removed faster. The stock therefore dries accordingly faster.

When a fibrous stock suspension is processed with the fiber loading technology, a completely new product results which possesses new and improved characteristics compared to the papers available on the market. The fiber loading process which is described below permits precipitation of a filler—especially calcium carbonate—which is uniformly distributed and adhered to, in and between the fibers directly in the stock preparation of a paper mill.

By way of a combination or by way of an individual application of the measures in accordance with the current invention described below, only precipitated calcium carbonate for the fiber loading process is produced and already present filler material is activated.

By utilizing the fiber loading technology in the pulper or in the batch-container, the optical characteristics of the paper suspension and the raw material can be improved by 0.5 to 30 lightness points, preferably by 1 to 25 lightness points—predominantly through masking of the contaminants such as ink particles and dirt. In addition, a conversion of non-activated fiber stock components, for example non-converted calcium hydroxide, PCC (precipitated calcium carbonate), GCC (ground calcium carbonate), lime components, etc. which are embedded in the recycled paper raw material or in the DIP-pulp occurs.

In accordance with one design form aqueous fiber raw material, especially aqueous paper raw material, having a consistency of between 1 and 20% of fibrous stock content is fed into the pressure vessel, wherein LC-fiber stock material (low consistency) is used at a content of between 1 and 6%, MC-fiber stock material (medium consistency) is used at a content of between 6 and 10%, and HC-fiber stock material (high consistency) is used at a content of between 10 and 20%.

It is advantageous if the aqueous fiber raw material is diluted to a fibrous stock suspension having a consistency of between 0.1 and 20%, especially diluted to a consistency of between 2 and 18%.

In a suitable embodiment of the method the pressure vessel is closed by a sluice after supplying the aqueous fiber stock material and/or the dilution water.

It is advantageous if the calcium hydroxide or the calcium oxide is mixed into the aqueous fiber stock in a range of between 0.1 and 60% of the existing solids content of the volume of the dry fiber stock.

The pH value is preferably between 6 and 11, especially between 6.5 and 10.5.

The reaction time is between 0.0005 and 30 minutes, especially in a range of between 0.05 and 10 minutes.

The calcium carbonate can be precipitated advantageously through adding the carbon dioxide in a pressure range of between 0 and 15 bar, especially between 0 and 6 bar.

One design form of the method provides that the fibrous stock suspension and/or the carbon dioxide is heated by way of process water or dilution water or steam during its dissolution in the fibrous stock suspension, or by way of the fiber loading process or through introducing heat energy from the outside, especially by way of steam energy or electrical energy.

The carbon dioxide can be added prior to, during or after the addition of the carbon dioxide or the calcium hydroxide or the calcium oxide.

In this connection it is advantageous if the pressure vessel is opened by a valve or a sluice before the fiber loading reaction, or after the reaction.

The energy expenditure for the precipitation of the loaded fibers is between 0.3 and 8 kWh/t, especially between 0.5 and 4 kWh/t, if no refiner for the fiber stock is used. A refiner may also be installed before the vessel if the fiber pulp is already sufficiently dissolved. In an alternative embodiment of the current invention the refiner may also be installed downstream from the pressure vessel.

The process temperature is preferably between −15° and 120°, especially between 20 and 90° C.

Due to the fiber loading process rhombohedral, scalenohedron and spherical crystals are formed.

Due to this process crystals having dimensions preferably of between 0.05 and 5 μm, especially between 0.3 and 2.5 μm can be produced.

Static and/or moving, especially rotating, mixing elements can be utilized for the purpose of mixing the fibrous stock suspension.

The process is preferably conducted in a pressure range of between 0 and 15 bar, especially between 0 and 6 bar.

In an embodiment according to the present invention, it is also possible to conduct a refining process in the pressure vessel, at the same time as the precipitation process.

The present invention also relates to a device for the implementation of the method.

In accordance with the present invention, the device is characterized in that it includes an infeed device for the supply of the fiber raw material, as well as a pressure vessel.

An advantageous embodiment of the device provides that the pressure vessel includes a sluice or a valve through which the fiber raw material is fed for the production of the fibrous stock suspension with loaded fibers. The pressure vessel can be equipped with inlets for dilution or press water, for calcium oxide or calcium hydroxide and for carbon dioxide.

In addition the pressure vessel includes a rotor for mixing the fibrous stock suspension.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing, wherein:

FIG. 1 illustrates a device for loading a fibrous stock suspension including cellulose fibers with calcium carbonate according to the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing, there is shown a fiber raw material which is supplied to a pressure vessel 2 through a supply pipe 1. In order to be able to establish and limit the supply volume a sluice 3 which is opened and closed via a motor driven closing mechanism is located between the supply pipe 1 and the pressure vessel 2.

Dilution water, calcium hydroxide in liquid or solid form or calcium oxide or chemicals are added through additional supply line connections 4, 5, 6 so that, if the raw fiber stock was initially supplied to a fill level 7, a filling of the pressure container 2 above this fill level 7 is formed, including the calcium hydroxide which serves the fiber loading process, together with the water and/or the dilution water in which it is dissolved.

In order to mix the fiber raw stock with the calcium hydroxide so that this penetrates into the fibers, a rotor 8 is supplied which includes a propeller wheel or similar device at the bottom and/or at a higher level of the pressure container 2. The rotor 8 is driven via a motor 9.

At least one inlet 10 can be provided in the lower area of the pressure container 2 for carbon dioxide through which the calcium hydroxide reacts to calcium carbonate. After the fiber raw material has been dissolved and loaded with calcium carbonate it is routed to a machine for the production of a fibrous web, through a discharge pipe 12 which is equipped with a valve 11.

In addition a measuring location 13 can be provided on pressure container 2 in order to measure the chemical composition of the content in said pressure container 2, especially to measure the pH value.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Component Identification

-   1 Supply pipe -   2 Pressure container -   3 Sluice -   4 Supply line connection -   5 Supply line connection -   6 Supply line connection -   7 Filling level -   8 Rotor -   9 Motor -   10 Inlet for carbon dioxide -   11 Valve -   12 Discharge pipe -   13 Measuring location 

1. A method for loading a fibrous stock suspension including a plurality of cellulose fibers with calcium carbonate, said method comprising the steps of: adding at least one of calcium hydroxide in one of liquid and dry form and calcium oxide into the fibrous stock suspension; adding carbon dioxide into the fibrous stock suspension; and precipitating calcium carbonate from said calcium hydroxide through said carbon dioxide in a pressurized vessel.
 2. The method in accordance with claim 1, further comprising the step of supplying an aqueous fiber raw material with a consistency of between 1 and 20% fiber stock component into said pressure vessel.
 3. The method in accordance with claim 2, wherein said aqueous fiber raw material is an aqueous paper raw material.
 4. The method in accordance with claim 2, wherein said fiber stock component includes a low consistency fiber stock material at a content of between 1 and 6%.
 5. The method in accordance with claim 2, wherein said fiber stock component includes a medium consistency fiber stock material at a content of between 6 and 10%.
 6. The method in accordance with claim 2, wherein said fiber stock component includes a high consistency fiber stock material at a content of between 10 and 20%.
 7. The method in accordance with claim 2, wherein said aqueous fiber raw material is diluted to the fibrous stock suspension having a consistency of between 0.1 and 20%.
 8. The method in accordance with claim 2, wherein said aqueous fiber raw material is diluted to the fibrous stock suspension having a consistency of between 2 and 18%.
 9. The method in accordance with claim 1, wherein said pressure vessel is closed by a sluice after introducing at least one of an aqueous fiber stock material and a dilution water.
 10. The method in accordance with claim 9, wherein at least one of said calcium hydroxide and said calcium oxide is mixed into said aqueous fiber stock material within a range of between 0.1 and 60% of an existing solids content of a volume of a dry fiber stock.
 11. The method in accordance with claim 10, wherein the method is carried out at a pH value of between 6 and
 11. 12. The method in accordance with claim 10, wherein the method is carried out at a pH value of between 6.5 and 10.5.
 13. The method in accordance with claim 10, wherein said calcium hydroxide includes a reactivity in a range of between 0.0005 and 30 minutes.
 14. The method in accordance with claim 10, wherein said calcium hydroxide includes a reactivity in a range of between 0.05 and 10 minutes.
 15. The method in accordance with claim 1, wherein said calcium carbonate is precipitated by adding said carbon dioxide within a pressure range of between 0 and 15 bar.
 16. The method in accordance with claim 1, wherein said calcium carbonate is precipitated by adding said carbon dioxide within a pressure range of between 0 and 6 bar.
 17. The method in accordance with claim 1, wherein at least one of the fibrous stock suspension and said carbon dioxide is heated by one of process water, dilution water, and steam during dissolution in the fibrous stock suspension.
 18. The method in accordance with claim 1, wherein at least one of the fibrous stock suspension and said carbon dioxide is heated by one of a fiber loading process and introducing heat energy from outside.
 19. The method in accordance with claim 1, wherein at least one of the fibrous stock suspension and said carbon dioxide is heated by one of a steam energy and an electrical energy.
 20. The method in accordance with claim 1, wherein said carbon dioxide is added one of prior to, during, and after adding one of said carbon dioxide, said calcium hydroxide, and said calcium oxide.
 21. The method in accordance with claim 1, wherein said pressure vessel is opened by one of a valve and a sluice one of prior to and after a fiber loading reaction.
 22. The method in accordance with claim 1, further comprising precipitating a plurality of loaded fibers, wherein an energy expenditure for said precipitating said plurality of loaded fibers is between 0.3 and 8 kWh/t.
 23. The method in accordance with claim 22 wherein no refiner is used for a refining of a fiber stock.
 24. The method in accordance with claim 22, further comprising the step of refining a fiber stock inside said pressure vessel during a precipitation process.
 25. The method in accordance with claim 1, further comprising precipitating a plurality of loaded fibers, wherein an energy expenditure for said precipitating said plurality of loaded fibers is between 0.5 and 4 kWh/t.
 26. The method in accordance with claim 25, wherein no refiner is used for a refining of a fiber stock.
 27. The method in accordance with claim 1, wherein a process temperature is between—15 and 120° C.
 28. The method in accordance with claim 1, wherein a process temperature is between 20 and 90° C.
 29. The method in accordance with claim 27, wherein a plurality of rhombohedral, scalenohedron, and spherical crystals are formed.
 30. The method in accordance with claim 29, wherein said plurality of crystals include dimensions of between 0.05 and 5 μm.
 31. The method in accordance with claim 29, wherein said plurality of crystals include dimensions of between 0.3 and 2.5 μm.
 32. The method in accordance with claim 1, further comprising mixing the fibrous stock suspension with at least one mixing element including at least one of a static and a moving mixing element.
 33. The method in accordance with claim 32, wherein said at least one mixing element includes a rotating mixing element.
 34. A device for loading a fibrous stock suspension including a plurality of cellulose fibers with calcium carbonate, said device comprising: an infeed device for supplying a fiber raw material; and a pressure vessel, the device configured for adding at least one of calcium hydroxide in one of liquid and dry form and calcium oxide into the fibrous stock suspension, adding carbon dioxide into the fibrous stock suspension, and precipitating calcium carbonate from said calcium hydroxide through said carbon dioxide in a pressurized vessel.
 35. The device in accordance with claim 34, wherein said pressure vessel includes one of a sluice and a valve configured for feeding through said fiber raw material for producing the fibrous stock suspension with a plurality of loaded fibers.
 36. The device in accordance with claim 34, wherein said pressure vessel includes a plurality of inlets for at least one of dilution water, press water, calcium oxide, calcium hydroxide, and carbon dioxide.
 37. The device in accordance with claim 34, wherein said pressure vessel includes a rotor for mixing the fibrous stock suspension. 